Originally Posted by r1horn
Engine beds in and engine having fall rebuild
I was just reading your build thread and looks very good especial the design of the transom.
I just finished converting a Cougar from outboard to inboard and was given a lot on help and advise on this forum.
I was looking at your engine mounts and just wanted to pass on some advise that I was given by the forum founder and may be worth you bearing in mind.
When a boat takes off and comes back down the force of the water stops the hull's downward motion very quickly, but the mass (or weight) of the engine still wants to travel in the same direction i.e. down and puts a massive load on the engine mounts.
I was told in racing this can be to to 50G's. I other words the mass or your engine up to 50 times its own weight. so if your engine is 300kg and you hit a wave hard enough and cause 50G's your engine will have a force of 15,000kg trying to make its way out of the bottom of your boat. I found this hard to believe but it is true and it is not unheard of rip the the side out of and engine block when racing.
So it is important to spread the loads caused by the mass of the engine throughout the full bottom area of the hull, using longitudinal and transverse frame structures. With the type of boat you have these would be tied into the transom and the floor.
One of the problems I had with this was that the frame on my boat are foam filled instead of wood, and although it still makes a rigid structure you cant just mount the engine directly onto it. So I had to make a further frame out of aluminum to spread the loads. However in your case as you are starting from scratch you could make a wooden longitudinal and transverse frame structure ans should be no need for a sub frame.
Its only my my opinion but if you make your engine mounts as you have after a couple of waves the engine may fall though the bottom of the boat.
Have attached some pictures showing the framework in my boat and the sub frame i made to make to distribute the load evenly through the foam cored structure.
Good luck with your project